Sound reproducer



July 11, 1961 G. c. VAN cAMP SOUND REPRODUCER Filed Sept. 12. 1957 ATTORNEYS.

BY m Mdm@ United States Patent C) 2,991,840 SOUND REPRODUCER Glenn C.Van Camp, West Palm Beach, Fla. (314 Armour Bldg., Worth Ave., PalmBeach, Fla.) Filed Sept. 12, 1957, Ser. No. 683,625 3 Claims. (Cl.181-31) This invention relates to sound reproduction and is for aso-called loud-speaker for reproducing a more realistic rendition of therecorded sounds, with particular reference to vibration in the bass endof the audible scale, that is vibrations below 250 c.p.s.

Loud-speaker cabinets generally, but not necessarily, comprise anenclosure having a front panel on which the cone speaker is mounted,with the interior of the cone facing outwardly. The other walls of thecabinet are variously formed of different materials in an attempt tosecure fidelity of reproduction. Most commonly plywood panels are usedwith heavy wood strips secured lthereto to reduce the resonance of thepanels. The enclosure is usually lined with hair felt or like materialto improve the tone qualities in the intermediate audible spectrum.

The diiculty of realistic reproduction occurs largely with vibrations inthe bass or lower frequency range and may be said to generally increasewith the decrease in pitch or frequency. This is largely attributed tothe fact that the negative wave phase generated at the rear of the conehas time to pass around the cone to the front and cancel the positivewave phase at the front. Ideally therefore, the best situation from thisstandpoint would be one in which the space at the rear of the cone'would be a room of comparable or Igreater volume than the room intowhich the cone faced. This is obviously impractical, but attempts aremade to provide very large cabinets, these often being of a sizeimpractical for many environments where recorded music is enjoyed, andeven with such enclosures the bass notes are likely to have anunna-tural boom or timbre. On the theory that the resonance of wood is afactor, some authorities have suggested concrete or brick as the bestenclosure, but this alone is not satisfactory and is highly impractical.It is also common practice to provide some bafiied channel arrangementto delay the back wave and bring it into isocronysm with the front wave,lbut this heavily accents the bass notes and requires expert design.

The present invention is based on dissipating the energy of the waveform within the cabinet by constructing the walls of the cabinet ofmaterial having substantially no resonance, and through which the airpulses generated by the speaker cone may pass, but with a great loss ofenergy. A condition approximating that of a room of large or infinitevolume is thereby approached. As a result, a cabinet of moderate sizemay be employed while securing a higher fidelity and much more realisticreproduction.

My invention may be more fully understood by reference to theaccompanying drawing, in which:

FIG. 1 is a vertical transverse sectional view through a speakerembodying my invention with the reproducing units schematically shown;and

FIG. 2 is a fragmentary detail sectional view on a large scale showing amodified wall construction.

In the drawing, 2 designates the fro-nt panel of a cabinet with a holetherein in which is set a cone speaker schematically illustrated anddesignated 3. Such speakers, as are well known, are formed with ashallow cone of a special moderately stiff paper, and of a diameter mostusually of about tifteen inches, although this varies widely. Theperiphery of the cone is secured in a frame and there is an armature atthe center which is operated by a coil through which the sound modulatedelectric current passes. This cone, upon being vibrated, alternately`moves the air to create sound waves. 'It may be regarded ICC in a senselike a pump that pushes the air over its surface in one direction andthen pulls it back, making it alternately -dense and rare, and when itis pushing at the front, it is drawing back at the rear face so that thewaves at the front and back are of equal, but opposite, phase.

In addition to the front panel, the cabinet here shown has a back wall4, side walls 5, and top and bottom walls 6 and 7 respectively, it beinggenerally cubical or rectangular, but it may be some other shape. Theremay be a skeleton framing of wood, plastic or other rigid material, theframing members being designated 8.

According to the present invention, each of the enclosure walls otherthan the front panel is formed of two or more spaced sheets 9 and 10 ofair-pervious felted or felt-like fabric, preferably one made fromvegetable fibers, such, for example, as ozte or similar floor paddingused under carpets. Other felted fibrous materials may be used, but thematerial should be soft and tiexible` The alternate dense and rare airconditions generated in the enclosure by the speaker can pass throughthis material, but the energy is greatly spent and the wave form isdisrupted. Since the material has little inherent resonance and absorbsthe energy, it does not vibrate as a diaphragm to any appreciableextent, nor refiect low frequency waves to a noticeably detrimentalextent.

The felted material of course does not completely deaden the sound, butby providing a second panel of like material with an intervening airspace, the deadening effeet on the pulsations at the back of the cone isentirely adequate to produce good tone quality and volume. It can beimproved by using additional felted layer of fibers separated from theothers by air spaces. This is indicated in FIG. 2 where three suchcurtains are provided in each enclosure wall other than the front panel,these being 9, 10, and 11, while 12 and 13 are the air spaces between.The material may be secured to the wooden frames 14 by any type ofconventional fastening and the frames are firmly fitted into the cabinetframing, and the fabric should be applied without stretching.

It is well recognized that intermediate and higher frequencies are welltaken care of in a cabinet of moderate size formed of plywood andcovered interiorly with hair felt, so my improved cabinet has no adverseeffects in the higher ranges.

Experimental cabinets utilizing my invention have been made withsubstantially less cubical volume than that recommended by the builderof the cone speaker, so that my invention not only achieves a truerfidelity, but effects a saving of space. It is unnecessary to providevents as is often done, and the size and location of which is critical.

It will be understood that I have disclosed one type of cabinetconstruction, but that it may be variously shaped, proportioned andframed within the contemplation of my invention.

I claim:

1. A loud speaker for sound reproduction comprising an enclosure havinga rigid front panel With a cone speaker mounted thereon, all of theremaining walls of the enclosure being each comprised of at least twospaced sheets of flexible, fibrous, sound-absorbing, substantiallynonresonant material pervious to the restricted passage of airtherethrough and an open rigid framework for the enclosure to which theedges only of said sheets are attached.

2. A loud speaker for sound reproduction comprising an open framestructure defining a cabinet, a single rigid panel enclosing one sideonly of the cabinet having a cone speaker mounted therein, the top andremaining side walls of the cabinet being each closed by a plurality ofcurtains with an air space between the curtains, the curtain being offlexible, fibrous, sound-absorbing, non-resonating ma- 3 terial attachedto the open framework only around the rigid open framework dening theboundaries of the cabedges of the sheets. inet walls to Iwhich the edgesonly of the sheets of ber 3. A loud speaker for sound reproductioncomprising are attached. a cabinet having a front panel in which ismounted a coney type loud speaker, th'e remaining walls of the cabinet 5References Cited in the le of this patent being enclosed by matted bersin sheet form pervious to restricted air 110W therethrough butsubstantially non-res- UNITED STATES PATENTS onant and sound-absorbtive,and capable of substantially 359,492 Balloch Mar. 15, 1887 damping theamplitude of low frequency pulsations gen- 1,811,985 VOlf a June 30,1931 erated in the cabinet by the vibration of the cone, and a 101,975,201 Elworthy Oct. 2, 1934

